I'd brown the chicken first in a little olive oil, and set them aside. In the same pan, saute your onions and mushrooms together, and right before they're done, add the garlic. Let that cook a bit, then add your chicken back into it and cook until your chicken is done. Do you have any canned tomatoes? You could make Chicken Cacciatore. Or serve this on a bed of sauteed spinach. Or add a can of chickpeas or white beans to it.
You have a good base, the possibilities are endless.